Directions

Cook the shells in generous amount of lightly salted boiling water until just tender; about 8 minutes.
While the pasta cooks, place the ricotta, egg, pesto and 2/3 of each of the mozzarella, asiago and Parmesan cheeses in a bowl. Mix to combine and season with nutmeg, salt and pepper.
When tender, drain the pasta, cool in cold water and drain again. Stuff a heaping tablespoon of ricotta mixture into each pasta shell and set in a single layer on a large baking sheet.
Place the tomato sauce and stock in a bowl and mix to combine. Divide the mixture amoung six single-serving dishes and place 4 shells in each one or two larger baking dishes, arrange 12 stuffed shells in each one.
Sprinkle the shells in each baking dish with some of the remaining mozzarella, asiago and Parmesan cheeses.
Tightly wrap, label, date and freeze until ready to use. When baking cover thawed shells with foil. Bake in 350 oven for 35 minutes. Uncover and bake 10-15 minutes more, or until golden on top and the sauce is bubbling.